1. Field of Invention
The present invention relates to an oscillator adaptable to various types of wireless remote control systems or various types of information processing systems, or more particularly, to an oscillator employing a surface acoustic wave resonator. The wireless remote control systems are usable to, for example, remotely manipulate various kinds of electronic equipment, or adaptable to a key-entry system for remotely opening or closing a door lock of a motor car.
2. Description of Related Art
The invention disclosed in, for example, Japanese Unexamined Patent Publication Application No. 11-17747 is known as one of related arts.
According to the related art, a transmitter for a key-entry system that serves as a communicator is constructed using a frequency-shift keying (FSK) modulator. Consequently, adjustment of a frequency and assembling of components are simplified, the costs of machining are reduced, and a low price is realized.
In the related art described above, the FSK modulator handles a single frequency. For realizing an FSK modulator for handling another frequency, all constants set in circuits must be corrected or reviewed accordingly. This can be inconvenient.
Moreover, according to the related art, a frequency band and communication method permitting the oscillator to act as a communicator are limited to specific ones. The oscillator may therefore be unusable for a wide range of applications.
Furthermore, according to the related art, an adjustment step at which a trimming pattern is employed is included in a manufacturing process. Mass-produced products must be adjusted one by one. This may pose a problem in that an increase in the costs of manufacturing is invited.
Furthermore, the related art has been devised on the assumption that an oscillator must meet the specifications defined by a specific user. This may pose a problem in that the oscillator cannot be flexibly and immediately retrofitted to be compatible with the specifications defined by various users (resonant frequency, transmission power, current consumption, etc.).
Accordingly, an object of the present invention is to at least provide an oscillator capable of being flexibly retrofitted to become usable for a wide range of applications and to become compatible with specifications defined by various users. Moreover, a user can adopt the oscillator without concern when designing a high-frequency unit. Besides, the oscillator enables saving of an occupied space and a reduction in costs.
According to an exemplary embodiment of this invention, an oscillator has at least a surface acoustic wave (SAW) resonator and an oscillation circuit for causing the SAW resonator to oscillate. The oscillator includes a negative resistance varying device for varying a negative resistance that affects the oscillations of the oscillation circuit, and an oscillatory output varying device for varying the intensity of an output of the oscillation circuit.
According to another exemplary embodiment, the negative resistance varying device included in the oscillator set forth above makes it possible to externally and independently adjust a reactance, which is offered by a reactive circuit and affects the oscillations of the oscillation circuit, and a current flowing through the oscillation circuit.
According to another exemplary embodiment, the reactive circuit included in the oscillator set forth above has a variable capacitive element as an integral part thereof.
According to another exemplary embodiment, the oscillation circuit included in the oscillator set forth above has a reactive circuit included in an oscillatory loop, which is realized in the form of an integrated circuit. Moreover, a reactance offered by the reactive circuit can be adjusted arbitrarily externally.
According to the above exemplary embodiments, the oscillator includes a negative resistance varying device for varying a negative resistance that affects the oscillations of the oscillation circuit, and an oscillatory output varying device for varying the intensity of an output of the oscillation circuit. Consequently, the negative resistance and the intensity of an oscillatory output can be optimized independently of each other at a user-requested resonant frequency. According to the above exemplary embodiments, the oscillator can be flexibly retrofitted to become usable for a wide range of applications and to become compatible with users""different requests.
The oscillation circuit above has the reactive circuit, which is realized in the form of an integrated circuit, included in the oscillatory loop. Moreover, the reactance of the reactive circuit can be adjusted externally arbitrarily. Consequently, a user can optimize the negative resistance of the oscillation circuit. Moreover, since the reactive circuit included in the oscillatory loop is realized in the form of an integrated circuit, a highly reliable oscillator can be realized to be unsusceptible to a stray capacitance introduced by any of circuit elements laid out according to a user-specific pattern. Furthermore, a user can design a high-frequency unit without concern, and will find the oscillator very helpful.
According to another exemplary embodiment, the oscillation circuit included in the oscillator set forth above has a modulating device for modulating an oscillatory output of the oscillation circuit according to a modulating signal.
According to another exemplary embodiment, a modulation form adopted by the modulating device included in the oscillator set forth above is at least one of the amplitude-shift keying (ASK) form and the frequency-shift keying (FSK) form.
According to the above exemplary embodiments, the inclusion of the modulating device provides the oscillator with the capability of a transmitter. Consequently, a low-cost oscillator usable for a wide range of applications can be provided for users.
According to another exemplary embodiment, the oscillation circuit included in the oscillator set forth above includes in an output stage thereof an output matching device for matching the impedance of the oscillator with the impedance of an external device.
According to the above exemplary embodiment, the output matching device for matching the electrical characteristic of the oscillator with that of an antenna is included in addition to the modulating device. The capability of a transmitter is improved.
According to another exemplary embodiment, the oscillation circuit in the oscillator set forth above includes in the output stage thereof a frequency multiplying device for multiplying the frequency of an output.
According to the above exemplary embodiment, the frequency multiplying device is included in addition to the modulating device. An oscillator oscillating in a wider frequency band, obviating user""s concern about designing, costing low, and being adaptable to a wide range of markets can be provided.
According to another exemplary embodiment, in the oscillator set forth above, among the SAW resonator, the oscillation circuit, the modulating device, the output matching device, and the frequency multiplying device, at least the SAW resonator, the oscillation circuit, and the modulating device are encapsulated in the same package.
According to the above exemplary embodiment, all the components are encapsulated in the same package. An oscillator or a transmitter can be realized with an occupied space and costs saved.
According to another exemplary embodiment, in the oscillator set forth above, among the SAW resonator, the oscillation circuit, the modulating device, the output matching device, and the frequency multiplying device, at least the SAW resonator, the oscillation circuit, and the modulating device are integrated into one circuit and encapsulated in the same package. The integration may result in an integrated circuit (IC) or a hybrid IC.
According to the above exemplary embodiment, predetermined components are integrated into one circuit and encapsulated in the same package. An oscillator or transmitter can be realized with an occupied space and costs saved.